LiDAR info topic

[drwnz]

In a ROSBag with only nebula_packets there is no way to know the LiDAR configuration that generated these packets.
Especially settings which change the pointcloud, like dual return settings, have to be known through also supplying the launchfile used with any ROSBag, for example.

Additionally, device-specific LiDAR calibration files are downloaded from the sensor or pre-downlaoded files read from disk, but the user has to manage the calibration files. Again, portability becomes an issue.

Therefore, we would like to propose a LiDAR info topic (something like the camera info topic) that periodically publishes the LiDAR calibration and configuration information. This requires adding a new message type as well. A static topic could also be considered but modifying and cutting ROSbags needs extra handling.